Potential as biological control agents of some novel epiphytic bacterial strains isolated from Italy

Several strains of epiphytic bacteria isolated from pear trees grown in commercial orchards in Italy were chosen for their ability to inhibit Erwinia amylovora on plate. The strains IPV-BO 4027C and IPV-BO 4027D were characterised according to their fatty acid profiles (FAMEs) and amplification and sequencing of their 16SrDNA gene. E. amylovora was not inhibited by these non fluorescent pseudomonads in the presence of FeCl3, suggesting that the inhibitory activity was due to a siderophore type activity. In the laboratory, both strains were able to colonise apple and pear flowers and were also able to reduce populations of E. amylovora on apple flowers. Experiments were carried out at Ruakura, New Zealand, to evaluate the ability of rifampicin resistant mutants (Rif(r)) of both strains to survive on apple flowers in the field: after seven days, the population level of 4027D Rif(r) was lower than that of the 4027C Rif(r) mutant (approx. 10(3) and 10(6) cfu/flower, respectively). When a local virulent strain of E. amylovora was sprayed one day after treatment with 4027C Rif(r) fire blight incidence was reduced by 45% while in the same experiment it was reduced by 92% when using streptomycin. The ability of 4027C Rif(r) to colonise pear and apple leaves was investigated by leaf imprints on plates of selective agar (LB-agar containing 20 gg/ml rifampicin).